1. Field of the Invention
The invention relates to the field of MOS computers.
2. Prior Art
MOS and bipolar multi-chip digital computers are known in the art. For example, a multi-chip bipolar microprocessor and a single chip MOS processor are commercially available. However, several other chips are required to fabricate a complete MOS computer from a single chip MOS processor. Typically, a separate chip or chips are required for program storage, "scratchpad" memory or other functions. By reducing the number of chips required to fabricate a computer, cost is reduced, compatibility problems are lessened, and cycle times are readily increased.
For many less sophisticated digital computer applications such as for automobiles, appliances, and countless other applications, a multi-chip computer is both too costly and overly complicated. Ideally, for many such applications, a single chip digital computer which includes program storage is needed.
Several problems result with the fabrication of an entire computer on a single chip or substrate. In prior art computers, for example, the program memory may be readily separated from the CPU, allowing independent testing of the CPU and program memory. However, when both the CPU and program memory are on the same chip, independent testing of the program memory and CPU becomes difficult. Other problems occur where an erasable PROM is employed in a single chip computer. Such PROM's require substantially higher programming voltages than are used during computer operation and such programming potentials may cause damage to parts of the computer.
Also to realize a single chip MOS computer, the "scratchpad" registers must be used to their maximum efficiency, since such registers require a considerable amount of chip area when compared to the other computer circuits.
As will be seen, the present invention provides an entire MOS computer including an erasable PROM on a single MOS chip. A RAM, which is used in a highly efficient manner, provides "scratchpad" storage.